Virtualization of a computing infrastructure such as that used for offering telephone communications services involves offering such services over a computing environment.
Virtualization may include the use of physical machines, servers and virtual machines. A physical machine or a server is a physical entity. A virtual machine includes software executing on a physical machine which emulates an independent and separate machine from other virtual machines which may be emulated on the same physical machine. A single physical machine may host multiple virtual machines. The term “server” may refer to either a physical machine or a virtual machine, based on context.
Virtual machines may be replicated using one of two methods. One is Synchronous Virtual Machine Replication and a second is Asynchronous Virtual Machine Replication. Synchronous Virtual Machine Replication is too slow to be practically useful for high data-rate applications. Asynchronous Virtual Machine Replication, although significantly better than the Synchronous solution, is not directly applicable to high data rate applications, because of the restrictions it imposes on outbound traffic (all transmitted packets need to be buffered for extended periods of time, resulting in significant bandwidth decrease).
Asynchronous replication guarantees that external clients have a consistent view of the replicated system regardless of failures. Primary and backup are only in sync at certain intervals. If all data packet transmissions happen for data packets that were created in the previous time interval, then the consistency is guaranteed, because the previous interval has been successfully committed to the backup.
Because all data packets are buffered in the known asynchronous methods, packets are only transmitted every default time interval (Tepoch), thus reducing effective bandwidth by a factor proportional to the duration of the interval. Further, in the known asynchronous methods outside clients will experience periods of inactivity during packet buffering followed by brief periods of very high network traffic during buffer release. Still further, in the known asynchronous methods a response from the replicated virtual machine will be delayed on average by Tepoch/2.